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Da'dara AA, Nation CS, Skelly PJ. Metabolism of FAD, FMN and riboflavin (vitamin B2) in the human parasitic blood fluke Schistosoma mansoni. BMC Infect Dis 2024; 24:636. [PMID: 38918706 PMCID: PMC11202380 DOI: 10.1186/s12879-024-09538-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2024] [Accepted: 06/19/2024] [Indexed: 06/27/2024] Open
Abstract
BACKGROUND Schistosomiasis is a parasitic disease caused by trematodes of the genus Schistosoma. The intravascular worms acquire the nutrients necessary for their survival from host blood. Since all animals are auxotrophic for riboflavin (vitamin B2), schistosomes too must import it to survive. Riboflavin is an essential component of the coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD); these support key functions of dozens of flavoenzymes. METHODS Here, using a combination of metabolomics, enzyme kinetics and in silico molecular analysis, we focus on the biochemistry of riboflavin and its metabolites in Schistosoma mansoni (Sm). RESULTS We show that when schistosomes are incubated in murine plasma, levels of FAD decrease over time while levels of FMN increase. We show that live schistosomes cleave exogenous FAD to generate FMN and this ability is significantly blocked when expression of the surface nucleotide pyrophosphatase/phosphodiesterase ectoenzyme SmNPP5 is suppressed using RNAi. Recombinant SmNPP5 cleaves FAD with a Km of 178 ± 5.9 µM and Kcat/Km of 324,734 ± 36,347 M- 1.S- 1. The FAD-dependent enzyme IL-4I1 drives the oxidative deamination of phenylalanine to produce phenylpyruvate and H2O2. Since schistosomes are damaged by H2O2, we determined if SmNPP5 could impede H2O2 production by blocking IL-4I1 action in vitro. We found that this was not the case; covalently bound FAD on IL-4I1 appears inaccessible to SmNPP5. We also report that live schistosomes can cleave exogenous FMN to generate riboflavin and this ability is significantly impeded when expression of a second surface ectoenzyme (alkaline phosphatase, SmAP) is suppressed. Recombinant SmAP cleaves FMN with a Km of 3.82 ± 0.58 mM and Kcat/Km of 1393 ± 347 M- 1.S- 1. CONCLUSIONS The sequential hydrolysis of FAD by tegumental ecto-enzymes SmNPP5 and SmAP can generate free vitamin B2 around the worms from where it can be conveniently imported by the recently described schistosome riboflavin transporter SmaRT. Finally, we identified in silico schistosome homologs of enzymes that are involved in intracellular vitamin B2 metabolism. These are riboflavin kinase (SmRFK) as well as FAD synthase (SmFADS); cDNAs encoding these two enzymes were cloned and sequenced. SmRFK is predicted to convert riboflavin to FMN while SmFADS could further act on FMN to regenerate FAD in order to facilitate robust vitamin B2-dependent metabolism in schistosomes.
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Affiliation(s)
- Akram A Da'dara
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, USA
| | - Catherine S Nation
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, USA
| | - Patrick J Skelly
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, USA.
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2
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Da'dara AA, Gondane R, Skelly PJ. The riboflavin (vitamin B2) transporter protein (SmaRT) of the human intravascular parasitic trematode Schistosoma mansoni. Heliyon 2024; 10:e28271. [PMID: 38601580 PMCID: PMC11004526 DOI: 10.1016/j.heliyon.2024.e28271] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2024] [Revised: 03/14/2024] [Accepted: 03/14/2024] [Indexed: 04/12/2024] Open
Abstract
Schistosomes are intravascular parasitic worms infecting >200 million people globally. Here we examine how the worms acquire an essential nutrient - vitamin B2 (riboflavin). We demonstrate that all intravascular life stages (schistosomula, adult males and females) take up radiolabeled riboflavin. This process is impeded in the presence of excess unlabeled riboflavin and at 4 °C. We have identified a transporter homolog in worms designated SmaRT (Schistosoma mansoni riboflavin transporter) that localizes to the tegument and internal tissues of adults. CHO-S cells transfected with plasmid encoding SmaRT import significantly more radiolabeled riboflavin compared to controls. Uptake of radiolabel is impeded when SmaRT-expressing cells are incubated in an excess of unlabeled riboflavin but not by an excess of an irrelevant metabolite. Uptake is mediated in a sodium-independent manner and over a wide range of pH values (pH 5.5-9). This is the first identification of a bone fide riboflavin transporter in any platyhelminth.
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Affiliation(s)
- Akram A. Da'dara
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, USA
| | - Roshni Gondane
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, USA
| | - Patrick J. Skelly
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, USA
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3
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Da’dara AA, Nation CS, Skelly PJ. Metabolism of FAD, FMN and riboflavin (vitamin B2) in the human parasitic blood fluke Schistosoma mansoni. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.03.12.584659. [PMID: 38558993 PMCID: PMC10980065 DOI: 10.1101/2024.03.12.584659] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/04/2024]
Abstract
Schistosomiasis is a parasitic disease caused by trematode worms of the genus Schistosoma. The intravascular worms acquire the nutrients necessary for their survival from host blood. Since all animals are auxotrophic for riboflavin (vitamin B2), schistosomes too must import it to survive. Riboflavin is an essential component of the coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD); these support key functions of dozens of flavoenzymes. In this work we focus on the biochemistry of riboflavin and its metabolites in Schistosoma mansoni. We show that when schistosomes are incubated in murine plasma, levels of FAD decrease over time while the levels of FMN increase. We show that live schistosomes can cleave exogenous FAD to generate FMN and this ability is significantly blocked when expression of the surface ectoenzyme SmNPP5 is suppressed using RNAi. Recombinant SmNPP5 cleaves FAD with a Km of 178 ± 5.9 µM. The FAD-dependent enzyme IL-4I1 drives the oxidative deamination of phenylalanine to produce phenylpyruvate and H2O2 in the extracellular environment. Since schistosomes can be damaged by H2O2, we determined if SmNPP5 could impede H2O2 production by blocking IL-4I1 action in vitro. We found that this was not the case, suggesting that covalently bound FAD on IL-4I1 is inaccessible to SmNPP5. We also report here that live schistosomes can cleave exogenous FMN to generate riboflavin and this ability is significantly impeded when expression of a second surface ectoenzyme (alkaline phosphatase, SmAP) is suppressed. Recombinant SmAP cleaves FMN with a Km of 3.82 ± 0.58 mM. Thus, the sequential hydrolysis of FAD by tegumental ecto-enzymes SmNPP5 and SmAP can generate free vitamin B2 around the worms from where it can be conveniently imported by, we hypothesize, the recently described schistosome riboflavin transporter SmaRT. In this work we also identified in silico schistosome homologs of enzymes that are involved in intracellular vitamin B2 metabolism. These are riboflavin kinase (SmRFK) as well as FAD synthase (SmFADS); cDNAs encoding these two enzymes were cloned and sequenced. SmRFK is predicted to convert riboflavin to FMN while SmFADS could further act on FMN to regenerate FAD in order to facilitate robust vitamin B2-dependent metabolism in schistosomes.
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Affiliation(s)
- Akram A. Da’dara
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, USA
| | - Catherine S. Nation
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, USA
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Rinaldi G, Paz Meseguer C, Cantacessi C, Cortés A. Form and Function in the Digenea, with an Emphasis on Host-Parasite and Parasite-Bacteria Interactions. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2024; 1454:3-45. [PMID: 39008262 DOI: 10.1007/978-3-031-60121-7_1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/16/2024]
Abstract
This review covers the general aspects of the anatomy and physiology of the major body systems in digenetic trematodes, with an emphasis on new knowledge of the area acquired since the publication of the second edition of this book in 2019. In addition to reporting on key recent advances in the morphology and physiology of tegumentary, sensory, neuromuscular, digestive, excretory, and reproductive systems, and their roles in host-parasite interactions, this edition includes a section discussing the known and putative roles of bacteria in digenean biology and physiology. Furthermore, a brief discussion of current trends in the development of novel treatment and control strategies based on a better understanding of the trematode body systems and associated bacteria is provided.
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Affiliation(s)
- Gabriel Rinaldi
- Department of Life Sciences, Edward Llwyd Building, Aberystwyth University, Aberystwyth, UK
| | - Carla Paz Meseguer
- Department of Pharmacy and Pharmaceutical Technology and Parasitology, School of Pharmacy and Food Sciences, Universitat de València, Valencia, Spain
| | - Cinzia Cantacessi
- Department of Veterinary Medicine, University of Cambridge, Cambridge, UK
| | - Alba Cortés
- Department of Pharmacy and Pharmaceutical Technology and Parasitology, School of Pharmacy and Food Sciences, Universitat de València, Valencia, Spain.
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Anwar FS, Abdel-Malek AR, Salem SH, Farouk M, Ali MF, Abdelrady YA, Sayed AM. In vitro and In silico assessment of antischistosomal activities of ethanolic extract of Cornulacamonacantha. Exp Parasitol 2023; 254:108631. [PMID: 37820894 DOI: 10.1016/j.exppara.2023.108631] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2023] [Revised: 08/28/2023] [Accepted: 10/08/2023] [Indexed: 10/13/2023]
Abstract
Schistosomiasis is the second most prevailing parasitic disease worldwide. Although praziquantel is considered an effective drug in the treatment against schistosomiasis to some extent, there is an emerging drug resistance that widely recorded. Therefore, there is an urgent need to develop effective and safe anti-schistosomal drugs. In this study, Cornulaca monacantha (C. monacantha), a sub-saharan plant, was extracted using aqueous ethanol and characterized by High-Performance Liquid Chromatography (HPLC). Major constituents of the extract are belonging to flavonoids, tannins and phenolic glycosides. Worms' viability and surface morphology of Schistosoma mansoni (S. mansoni) adult worms treated with the extract were assessed using in vitro viability assay, Scanning Electron Microscopy (SEM), and histological examination. The extract (80-350 μg/ml) reduced viability percentage of worms by 40-60% and caused degeneration of both oral and ventral suckers, tegumental, sub-tegumental and muscular damage. Molecular docking approach was utilized to assess the binding affinities of the extracted compounds with S. mansoni alpha-carbonic anhydrase (SmCA), an essential tegument protein. Pharmacokinetic analysis using SwissADME showed that 7 compounds have high drug similarity. This study confirms the in vitro schistomicidal activity of C. monacantha extract against S. mansoni adult worms and suggests potential SmCA inhibition.
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Affiliation(s)
- FatmaA S Anwar
- Zoology Department, Faculty of Science, Assiut University, 71516, Egypt
| | | | - Shimaa H Salem
- Botany and Microbiology Department, Faculty of Science, Assiut University, 71516, Egypt
| | - Mohamed Farouk
- Department of Tropical Medicine and Gastroenterology, Faculty of Medicine, New Valley University, 72511, Egypt
| | - Marwa F Ali
- Department of Pathology and Clinical Pathology, Faculty of Veterinary Medicine, Assiut University, Egypt
| | - Yousef A Abdelrady
- Faculty of Pharmacy, Assiut University, Assiut, 71526, Egypt; University of Hamburg, Institute of Pharmacy, 20146, Germany
| | - Ahmed M Sayed
- Biochemistry Laboratory, Chemistry Department, Faculty of Science, Assiut University, 71516, Egypt.
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6
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Skelly PJ, Da'dara AA. A novel, non-neuronal acetylcholinesterase of schistosome parasites is essential for definitive host infection. Front Immunol 2023; 14:1056469. [PMID: 36798133 PMCID: PMC9927205 DOI: 10.3389/fimmu.2023.1056469] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2022] [Accepted: 01/16/2023] [Indexed: 02/03/2023] Open
Abstract
Schistosomes are long-lived parasitic worms that infect >200 million people globally. The intravascular life stages are known to display acetylcholinesterase (AChE) activity internally as well as, somewhat surprisingly, on external tegumental membranes. Originally it was hypothesized that a single gene (SmAChE1 in Schistosoma mansoni) encoded both forms of the enzyme. Here, we demonstrate that a second gene, designated "S. mansoni tegumental acetylcholinesterase, SmTAChE", is responsible for surface, non-neuronal AChE activity. The SmTAChE protein is GPI-anchored and contains all essential amino acids necessary for function. AChE surface activity is significantly diminished following SmTAChE gene suppression using RNAi, but not following SmAChE1 gene suppression. Suppressing SmTAChE significantly impairs the ability of parasites to establish infection in mice, showing that SmTAChE performs an essential function for the worms in vivo. Living S. haematobium and S. japonicum parasites also display strong surface AChE activity, and we have cloned SmTAChE homologs from these two species. This work helps to clarify longstanding confusion regarding schistosome AChEs and paves the way for novel therapeutics for schistosomiasis.
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Affiliation(s)
- Patrick J Skelly
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, United States
| | - Akram A Da'dara
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, United States
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Skelly PJ, Nation CS, Da'Dara AA. Schistosoma mansoni and the purinergic halo. Trends Parasitol 2022; 38:1080-1088. [PMID: 36182536 PMCID: PMC9669209 DOI: 10.1016/j.pt.2022.09.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2022] [Revised: 08/25/2022] [Accepted: 09/02/2022] [Indexed: 01/13/2023]
Abstract
Intravascular schistosomes may control immune and hemostatic responses by regulating the nature and amount of selected host purinergic signaling molecules - such as adenosine triphosphate (ATP), adenosine diphosphate (ADP), and nicotinamide adenine dinucleotide (NAD) - surrounding them. Such metabolites are collectively known as the worm's 'purinergic halo'. Host-interactive, membrane-bound, tegumental ectonucleotidases, notably SmATPDase1, SmNPP5, SmAP and SmNACE, can degrade proinflammatory, prothrombotic and immunomodulatory purinergic metabolites like those listed. A common catabolic product is the anti-inflammatory metabolite adenosine that can additionally be taken in by the worms as food. We envision the tegumental ectonucleotidases as having a twofold role at the worm surface: first, they degrade potentially harmful host signaling molecules, and second, they generate vital nutrients around the worms from where these can be conveniently imported.
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Affiliation(s)
- Patrick J Skelly
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536, USA.
| | - Catherine S Nation
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536, USA
| | - Akram A Da'Dara
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536, USA
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Wendt GR, Shiroor DA, Adler CE, Collins JJ. Convergent evolution of a genotoxic stress response in a parasite-specific p53 homolog. Proc Natl Acad Sci U S A 2022; 119:e2205201119. [PMID: 36067283 PMCID: PMC9478680 DOI: 10.1073/pnas.2205201119] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2022] [Accepted: 08/08/2022] [Indexed: 11/18/2022] Open
Abstract
P53 is a widely studied tumor suppressor that plays important roles in cell-cycle regulation, cell death, and DNA damage repair. P53 is found throughout metazoans, even in invertebrates that do not develop malignancies. The prevailing theory for why these invertebrates possess a tumor suppressor is that P53 originally evolved to protect the germline of early metazoans from genotoxic stress such as ultraviolet radiation. This theory is largely based upon functional data from only three invertebrates, omitting important groups of animals including flatworms. Previous studies in the freshwater planarian flatworm Schmidtea mediterranea suggested that flatworm P53 plays an important role in stem cell maintenance and skin production, but these studies did not directly test for any tumor suppressor functions. To better understand the function of P53 homologs across diverse flatworms, we examined the function of two different P53 homologs in the parasitic flatworm Schistosoma mansoni. The first P53 homolog (p53-1) is orthologous to S. mediterranea P53(Smed-p53) and human TP53 and regulates flatworm stem cell maintenance and skin production. The second P53 homolog (p53-2) is a parasite-specific paralog that is conserved across parasitic flatworms and is required for the normal response to genotoxic stress in S. mansoni. We then found that Smed-p53 does not seem to play any role in the planarian response to genotoxic stress. The existence of this parasite-specific paralog that bears a tumor suppressor-like function in parasitic flatworms implies that the ability to respond to genotoxic stress in parasitic flatworms may have arisen from convergent evolution.
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Affiliation(s)
- George R. Wendt
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75235
| | - Divya A. Shiroor
- Department of Molecular Medicine, Cornell University College of Veterinary Medicine, Ithaca, NY 14853
| | - Carolyn E. Adler
- Department of Molecular Medicine, Cornell University College of Veterinary Medicine, Ithaca, NY 14853
| | - James J. Collins
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75235
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NAD-catabolizing ectoenzymes of Schistosoma mansoni. Biochem J 2022; 479:1165-1180. [PMID: 35593185 DOI: 10.1042/bcj20210784] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2021] [Revised: 05/18/2022] [Accepted: 05/20/2022] [Indexed: 11/17/2022]
Abstract
Infection with schistosomes (blood flukes) can result in the debilitating disease schistosomiasis. These parasites survive in their host for many years, and we hypothesize that proteins on their tegumental surface, interacting with the host microenvironment, facilitate longevity. One such ectoenzyme - the nucleotide pyrophosphatase/phosphodiesterase SmNPP5 can cleave ADP (to prevent platelet aggregation) and NAD (likely preventing Treg apoptosis). A second tegumental ectoenzyme, the glycohydrolase SmNACE, also catabolizes NAD. Here, we undertake a comparative biochemical characterization of these parasite ectoenzymes. Both are GPI-linked and exhibit different optimal pH ranges. While SmNPP5 requires divalent cations, SmNACE does not. The Km values of the two enzymes for NAD at physiological pH differ: SmNPP5, Km=340µM±44; SmNACE, Km=49µM±4. NAD cleavage by each enzyme yields different products. SmNPP5 cleaves NAD to form nicotinamide mononucleotide (NMN) and AMP, whereas SmNACE cleaves NAD to generate nicotinamide (NAM) and adenosine diphosphate ribose (ADPR). Each enzyme can process the other's reaction product. Thus, SmNACE cleaves NMN (to yield NAM and ribose phosphate) and SmNPP5 cleaves ADPR (yielding AMP and ribose phosphate). Metabolomic analysis of plasma containing adult worms supports the idea that these cleavage pathways are active in vivo. We hypothesize that a primary function of SmNPP5 is to cleave NAD to control host immune cell function and a primary function of SmNACE is to cleave NMN to generate the vital nutrient nicotinamide (vitamin B3) for convenient uptake by the worms. Chemical inhibition of one or both ectoenzymes could upset worm metabolism and control schistosome infection.
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Nation CS, Da’dara AA, Elzoheiry M, Skelly PJ. Schistosomes Impede ATP-Induced T Cell Apoptosis In Vitro: The Role of Ectoenzyme SmNPP5. Pathogens 2022; 11:pathogens11020155. [PMID: 35215099 PMCID: PMC8878264 DOI: 10.3390/pathogens11020155] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2021] [Revised: 01/18/2022] [Accepted: 01/22/2022] [Indexed: 02/08/2023] Open
Abstract
Schistosomes (blood flukes) can survive in the bloodstream of their hosts for many years. We hypothesize that proteins on their host-interactive surface impinge on host biochemistry to help ensure their long-term survival. Here, we focus on a surface ectoenzyme of Schistosoma mansoni, designated SmNPP5. This ~53 kDa glycoprotein is a nucleotide pyrophosphatase/phosphodiesterase that has been previously shown to: (1) cleave adenosine diphosphate (ADP) and block platelet aggregation; and (2) cleave nicotinamide adenine dinucleotide (NAD) and block NAD-induced T cell apoptosis in vitro. T cell apoptosis can additionally be driven by extracellular adenosine triphosphate (ATP). In this work, we show that adult S. mansoni parasites can inhibit this process. Further, we demonstrate that recombinant SmNPP5 alone can both cleave ATP and impede ATP-induced T cell killing. As immunomodulatory regulatory T cells (Tregs) are especially prone to the induction of these apoptotic pathways, we hypothesize that the schistosome cleavage of both NAD and ATP promotes Treg survival and this helps to create a less immunologically hostile environment for the worms in vivo.
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Abstract
Schistosomes are long lived, intravascular parasitic platyhelminths that infect >200 million people globally. The molecular mechanisms used by these blood flukes to dampen host immune responses are described in this review. Adult worms express a collection of host-interactive tegumental ectoenzymes that can cleave host signaling molecules such as the "alarmin" ATP (cleaved by SmATPDase1), the platelet activator ADP (SmATPDase1, SmNPP5), and can convert AMP into the anti-inflammatory mediator adenosine (SmAP). SmAP can additionally cleave the lipid immunomodulator sphingosine-1-phosphate and the proinflammatory anionic polymer, polyP. In addition, the worms release a barrage of proteins (e.g., SmCB1, SjHSP70, cyclophilin A) that can impinge on immune cell function. Parasite eggs also release their own immunoregulatory proteins (e.g., IPSE/α1, omega1, SmCKBP) as do invasive cercariae (e.g., Sm16, Sj16). Some schistosome glycans (e.g., LNFPIII, LNnT) and lipids (e.g., Lyso-PS, LPC), produced by several life stages, likewise affect immune cell responses. The parasites not only produce eicosanoids (e.g., PGE2, PGD2-that can be anti-inflammatory) but can also induce host cells to release these metabolites. Finally, the worms release extracellular vesicles (EVs) containing microRNAs, and these too have been shown to skew host cell metabolism. Thus, schistosomes employ an array of biomolecules-protein, lipid, glycan, nucleic acid, and more, to bend host biochemistry to their liking. Many of the listed molecules have been individually shown capable of inducing aspects of the polarized Th2 response seen following infection (with the generation of regulatory T cells (Tregs), regulatory B cells (Bregs) and anti-inflammatory, alternatively activated (M2) macrophages). Precisely how host cells integrate the impact of these myriad parasite products following natural infection is not known. Several of the schistosome immunomodulators described here are in development as novel therapeutics against autoimmune, inflammatory, and other, nonparasitic, diseases.
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Affiliation(s)
- Sreemoyee Acharya
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, Massachusetts, United States of America
| | - Akram A. Da’dara
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, Massachusetts, United States of America
| | - Patrick J. Skelly
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, Massachusetts, United States of America
- * E-mail:
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Schistosoma mansoni Adult Worm Protective and Diagnostic Proteins in n-Butanol Extracts Revealed by Proteomic Analysis. Pathogens 2021; 11:pathogens11010022. [PMID: 35055970 PMCID: PMC8777762 DOI: 10.3390/pathogens11010022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Revised: 12/09/2021] [Accepted: 12/21/2021] [Indexed: 12/02/2022] Open
Abstract
The S. mansoni adult worm n-butanol extract (Sm-AWBE) has been previously shown to contain specific S. mansoni antigens that have been used for immunodiagnosis of schistosomiasis in solid phase alkaline phosphatase immunoassay (APIA) and western blot (WB) analyses. Sm-AWBE was also used in immunoprotection studies against a fatal live-cercariae challenge in experimental mouse vaccination (~43% protection). The Sm-AWBE fraction was prepared by mixing adult worm membranous suspensions with aqueous-saturated n-butanol, centrifuging and recovering n-butanol-resistant proteins in the aqueous phase. Here we report a preliminary identification of Sm-AWBE protein components as revealed from a qualitative proteomic study after processing Sm-AWBE by 1D-gel electrophoresis, in-gel and in-solution tryptic digestions, and mass spectrometry analyses. We identified 33 proteins in Sm-AWBE, all previously known S. mansoni proteins and antigens; among them, immunomodulatory proteins and proteins mostly involved in host–parasite interactions. About 81.8% of the identified Sm-AWBE proteins are antigenic. STRING analysis showed a set of Sm-AWBE proteins configuring a small network of interactive proteins and a group of proteins without interactions. Functional groups of proteins included muscle contraction, antioxidant, GPI-anchored phosphoesterases, regulatory 14-3-3, various enzymes and stress proteins. The results widen the possibilities to design novel antigen combinations for better diagnostic and immunoprotective strategies for schistosomiasis control.
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Ndolo SM, Zachariah M, Molefi L, Phaladze N, Sichilongo KF. Mass spectrometry based metabolomics for small molecule metabolites mining and confirmation as potential biomarkers for schistosomiasis - case of the Okavango Delta communities in Botswana. Expert Rev Proteomics 2021; 19:61-71. [PMID: 34846232 DOI: 10.1080/14789450.2021.2012454] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
INTRODUCTION Metabolomics for identifying schistosomiasis biomarkers in noninvasive samples at various infection stages is being actively explored. The literature on the traditional detection of schistosomiasis in human specimens is well documented. However, state-of-the-art technologies based on mass spectrometry have simplified the use of biomarkers for diagnostics. This review examines methods currently in use for the metabolomics of small molecules using separation science and mass spectrometry. AREA COVERED This article highlights the evolution of traditional diagnostic methods for schistosomiasis based on inter alia microscopy, immunology, and polymerase chain reaction. An exhaustive literature search of metabolite mining, focusing on separation science and mass spectrometry, is presented. A comparative analysis of mass spectrometry methods was undertaken, including a projection for the future. EXPERT COMMENTARY Mass spectrometry metabolomics for schistosomiasis will lead to biomarker discovery for noninvasive human samples. These biomarkers, together with those from other neglected tropical diseases, such as malaria and sleeping sickness, could be incorporated as arrays on a single biosensor chip and inserted into smartphones, in order to improve surveillance, monitoring, and management.
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Affiliation(s)
- Sedireng M Ndolo
- College of Open Schooling, Botswana Open University, Gaborone Regional Campus, Gaborone, Botswana
| | - Matshediso Zachariah
- School of Allied Health Professions, Faculty of Health Sciences, University of Botswana, Gaborone, Botswana
| | - Lebotse Molefi
- School of Allied Health Professions, Faculty of Health Sciences, University of Botswana, Gaborone, Botswana
| | - Nthabiseng Phaladze
- School of Nursing, Faculty of Health Sciences, University of Botswana, Gaborone, Botswana
| | - Kwenga F Sichilongo
- Chemistry Department, Faculty of Science, University of Botswana, Gaborone, Botswana
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Fifty years of the schistosome tegument: discoveries, controversies, and outstanding questions. Int J Parasitol 2021; 51:1213-1232. [PMID: 34767805 DOI: 10.1016/j.ijpara.2021.11.002] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2021] [Revised: 11/01/2021] [Accepted: 11/01/2021] [Indexed: 11/21/2022]
Abstract
The unique multilaminate appearance of the tegument surface of schistosomes was first described in 1973, in one of the earliest volumes of the International Journal for Parasitology. The present review, published almost 50 years later, traces the development of our knowledge of the tegument, starting with those earliest cytological advances, particularly the surface plasma membrane-membranocalyx complex, through an era of protein discovery to the modern age of protein characterization, aided by proteomics. More recently, analysis of single cell transcriptomes of schistosomes is providing insight into the organisation of the cell bodies that support the surface syncytium. Our understanding of the tegument, notably the nature of the proteins present within the plasma membrane and membranocalyx, has provided insights into how the schistosomes interact with their hosts but many aspects of how the tegument functions remain unanswered. Among the unresolved aspects are those concerned with maintenance and renewal of the surface membrane complex, and whether surface proteins and membrane components are recycled. Current controversies arising from investigations about whether the tegument is a source of extracellular vesicles during parasitism, and if it is covered with glycolytic enzymes, are evaluated in the light of cytological and proteomic knowledge of the layer.
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Da’dara AA, Elzoheiry M, El-Beshbishi SN, Skelly PJ. Vitamin B6 Acquisition and Metabolism in Schistosoma mansoni. Front Immunol 2021; 11:622162. [PMID: 33613557 PMCID: PMC7891054 DOI: 10.3389/fimmu.2020.622162] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Accepted: 12/17/2020] [Indexed: 11/13/2022] Open
Abstract
Schistosomes are parasitic platyhelminths that currently infect >200 million people globally. The adult worms can live within the vasculature of their hosts for many years where they acquire all nutrients necessary for their survival and growth. In this work we focus on how Schistosoma mansoni parasites acquire and metabolize vitamin B6, whose active form is pyridoxal phosphate (PLP). We show here that live intravascular stage parasites (schistosomula and adult males and females) can cleave exogenous PLP to liberate pyridoxal. Of the three characterized nucleotide-metabolizing ectoenzymes expressed at the schistosome surface (SmAP, SmNPP5, and SmATPDase1), only SmAP hydrolyzes PLP. Heat-inactivated recombinant SmAP can no longer cleave PLP. Further, parasites whose SmAP gene has been suppressed by RNAi are significantly impaired in their ability to cleave PLP compared to controls. When schistosomes are incubated in murine plasma, they alter its metabolomic profile-the levels of both pyridoxal and phosphate increase over time, a finding consistent with the action of host-exposed SmAP acting on PLP. We hypothesize that SmAP-mediated dephosphorylation of PLP generates a pool of pyridoxal around the worms that can be conveniently taken in by the parasites to participate in essential, vitamin B6-driven metabolism. In addition, since host PLP-dependent enzymes play active roles in inflammatory processes, parasite-mediated cleavage of this metabolite may serve to limit parasite-damaging inflammation. In this work we also identified schistosome homologs of enzymes that are involved in intracellular vitamin B6 metabolism. These are pyridoxal kinase (SmPK) as well as pyridoxal phosphate phosphatase (SmPLP-Ph) and pyridox(am)ine 5'-phosphate oxidase (SmPNPO) and cDNAs encoding these three enzymes were cloned and sequenced. The three genes encoding these enzymes all display high relative expression in schistosomula and adult worms suggestive of robust vitamin B6 metabolism in the intravascular life stages.
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Affiliation(s)
- Akram A. Da’dara
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, United States
| | - Manal Elzoheiry
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, United States
- Department of Medical Parasitology, Faculty of Medicine, Mansoura University, Mansoura, Egypt
| | - Samar N. El-Beshbishi
- Department of Medical Parasitology, Faculty of Medicine, Mansoura University, Mansoura, Egypt
| | - Patrick J. Skelly
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, United States
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Pirovich DB, Da'dara AA, Skelly PJ. Schistosoma mansoni glyceraldehyde-3-phosphate dehydrogenase enhances formation of the blood-clot lysis protein plasmin. Biol Open 2020; 9:bio050385. [PMID: 32098782 PMCID: PMC7104858 DOI: 10.1242/bio.050385] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2019] [Accepted: 02/11/2020] [Indexed: 12/19/2022] Open
Abstract
Schistosomes are intravascular blood flukes that cause the parasitic disease schistosomiasis. In agreement with Schistosoma mansoni (Sm) proteomic analysis, we show here that the normally intracellular glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is also found at the parasite surface; live worms from all intravascular life stages display GAPDH activity. Suppressing GAPDH gene expression using RNA interference significantly lowers this live worm surface activity. Medium in which the worms are cultured overnight displays essentially no activity, showing that the enzyme is not shed or excreted but remains associated with the worm surface. Immunolocalization experiments confirm that the enzyme is highly expressed in the parasite tegument (skin). Surface activity in schistosomula amounts to ∼8% of that displayed by equivalent parasite lysates. To address the functional role of SmGAPDH, we purified the protein following its expression in Escherichiacoli strain DS113. The recombinant protein displays optimal enzymatic activity at pH 9.2, shows robust activity at the temperature of the parasite's hosts, and has a Michaelis-Menten constant for glyceraldehyde-3-phosphate (GAP) of 1.4 mM±0.24. We show that recombinant SmGAPDH binds plasminogen (PLMG) and promotes PLMG conversion to its active form (plasmin) in a dose response in the presence of tissue plasminogen activator. Since plasmin is a key mediator of thrombolysis, our results support the hypothesis that SmGAPDH, a host-interactive tegumental protein that can enhance PLMG activation, could help degrade blood clots around the worms in the vascular microenvironment and thus promote parasite survival in vivoThis article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- David B Pirovich
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536, USA
| | - Akram A Da'dara
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536, USA
| | - Patrick J Skelly
- Molecular Helminthology Laboratory, Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA 01536, USA
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Adekiya TA, Kondiah PPD, Choonara YE, Kumar P, Pillay V. A Review of Nanotechnology for Targeted Anti-schistosomal Therapy. Front Bioeng Biotechnol 2020; 8:32. [PMID: 32083071 PMCID: PMC7005470 DOI: 10.3389/fbioe.2020.00032] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2019] [Accepted: 01/14/2020] [Indexed: 12/15/2022] Open
Abstract
Schistosomiasis is one of the major parasitic diseases and second most prevalent among the group of neglected diseases. The prevalence of schistosomiasis may be due to environmental and socio-economic factors, as well as the unavailability of vaccines for schistosomiasis. To date, current treatment; mainly the drug praziquantel (PZQ), has not been effective in treating the early forms of schistosome species. The development of drug resistance has been documented in several regions globally, due to the overuse of PZQ, rate of parasitic mutation, poor treatment compliance, co-infection with different strains of schistosomes and the overall parasite load. Hence, exploring the schistosome tegument may be a potential focus for the design and development of targeted anti-schistosomal therapy, with higher bioavailability as molecular targets using nanotechnology. This review aims to provide a concise incursion on the use of various advance approaches to achieve targeted anti-schistosomal therapy, mainly through the use of nano-enabled drug delivery systems. It also assimilates the molecular structure and function of the schistosome tegument and highlights the potential molecular targets found on the tegument, for effective specific interaction with receptors for more efficacious anti-schistosomal therapy.
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Affiliation(s)
| | | | | | | | - Viness Pillay
- Wits Advanced Drug Delivery Platform Research Unit, Department of Pharmacy and Pharmacology, School of Therapeutic Science, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
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Pirovich D, Da'dara AA, Skelly PJ. Why Do Intravascular Schistosomes Coat Themselves in Glycolytic Enzymes? Bioessays 2019; 41:e1900103. [PMID: 31661165 DOI: 10.1002/bies.201900103] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Revised: 09/16/2019] [Indexed: 11/11/2022]
Abstract
Schistosomes are intravascular parasitic helminths (blood flukes) that infect more than 200 million people globally. Proteomic analysis of the tegument (skin) of these worms has revealed the surprising presence of glycolytic enzymes on the parasite's external surface. Immunolocalization data as well as enzyme activity displayed by live worms confirm that functional glycolytic enzymes are indeed expressed at the host-parasite interface. Since these enzymes are traditionally considered to function intracellularly to drive glycolysis, in an extracellular location they are hypothesized to engage in novel "moonlighting" functions such as immune modulation and blood clot dissolution that promote parasite survival. For instance, several glycolytic enzymes can interact with plasminogen and promote its activation to the thrombolytic plasmin; some can inhibit complement function; some induce B cell proliferation or macrophage apoptosis. Several pathogenic bacteria and protists also express glycolytic enzymes externally, suggesting that moonlighting functions of extracellular glycolytic enzymes can contribute broadly to pathogen virulence. Also see the video abstract here https://youtu.be/njtWZ2y3k_I.
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Affiliation(s)
- David Pirovich
- Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, 01536, USA
| | - Akram A Da'dara
- Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, 01536, USA
| | - Patrick J Skelly
- Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, 01536, USA
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Crystal structure and chemical inhibition of essential schistosome host-interactive virulence factor carbonic anhydrase SmCA. Commun Biol 2019; 2:333. [PMID: 31508507 PMCID: PMC6728359 DOI: 10.1038/s42003-019-0578-0] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2019] [Accepted: 08/13/2019] [Indexed: 01/06/2023] Open
Abstract
The intravascular parasitic worm Schistosoma mansoni is a causative agent of schistosomiasis, a disease of great global public health significance. Here we identify an α-carbonic anhydrase (SmCA) that is expressed at the schistosome surface as determined by activity assays and immunofluorescence/immunogold localization. Suppressing SmCA expression by RNAi significantly impairs the ability of larval parasites to infect mice, validating SmCA as a rational drug target. Purified, recombinant SmCA possesses extremely rapid CO2 hydration kinetics (kcat: 1.2 × 106 s-1; kcat/Km: 1.3 × 108 M-1s-1). The enzyme’s crystal structure was determined at 1.75 Å resolution and a collection of sulfonamides and anions were tested for their ability to impede rSmCA action. Several compounds (phenylarsonic acid, phenylbaronic acid, sulfamide) exhibited favorable Kis for SmCA versus two human isoforms. Such selective rSmCA inhibitors could form the basis of urgently needed new drugs that block essential schistosome metabolism, blunt parasite virulence and debilitate these important global pathogens. Akram Da’dara et al. report the biochemical characterization of an α-carbonic anhydrase (SmCA) expressed at the surface of the parasitic worm Schistosoma mansoni. Along with the crystal structure of SmCA, they show the function of selective inhibitors in blocking essential schistosome metabolism.
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Elzoheiry M, Da'dara AA, Nation CS, El-Beshbishi SN, Skelly PJ. Schistosomes can hydrolyze proinflammatory and prothrombotic polyphosphate (polyP) via tegumental alkaline phosphatase, SmAP. Mol Biochem Parasitol 2019; 232:111190. [PMID: 31154018 PMCID: PMC6717558 DOI: 10.1016/j.molbiopara.2019.111190] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2019] [Revised: 05/16/2019] [Accepted: 05/28/2019] [Indexed: 12/18/2022]
Abstract
Schistosoma mansoni is a long-lived intravascular trematode parasite that can infect humans causing the chronic debilitating disease, schistosomiasis. We hypothesize that the action of host-interactive proteins found at the schistosome surface allows the worms to maintain a safe, anti-thrombotic and anti-inflammatory environment around them in the bloodstream. One such protein is the ˜60 kDa alkaline phosphatase SmAP which is known to be expressed in the outer tegument of all intravascular life stages. We demonstrate in this work that the parasites (schistosomula as well as adult males and females) can hydrolyze polyphosphate (polyP) - an anionic, linear polymer of inorganic phosphates that is produced and released by immune cells as well as by activated platelets and that induce proinflammatory and prothrombotic pathways. Purified recombinant SmAP can likewise cleave polyP and with a Km of 6.9 ± 1 mM. Finally, parasites whose SmAP gene has been suppressed by RNAi are significantly impaired in their ability to hydrolyze polyP. SmAP-mediated cleavage of polyP may contribute to the armamentarium of schistosomes that promotes their survival in the hostile intravascular habitat. This is the first report of any pathogen cleaving this bioactive metabolite.
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Affiliation(s)
- Manal Elzoheiry
- Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, USA; Department of Medical Parasitology, Faculty of Medicine, Mansoura University, Egypt
| | - Akram A Da'dara
- Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, USA
| | - Catherine S Nation
- Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, USA
| | - Samar N El-Beshbishi
- Department of Medical Parasitology, Faculty of Medicine, Mansoura University, Egypt
| | - Patrick J Skelly
- Department of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University, North Grafton, MA, USA.
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Costain AH, MacDonald AS, Smits HH. Schistosome Egg Migration: Mechanisms, Pathogenesis and Host Immune Responses. Front Immunol 2018; 9:3042. [PMID: 30619372 PMCID: PMC6306409 DOI: 10.3389/fimmu.2018.03042] [Citation(s) in RCA: 112] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2018] [Accepted: 12/10/2018] [Indexed: 12/22/2022] Open
Abstract
Many parasitic worms possess complex and intriguing life cycles, and schistosomes are no exception. To exit the human body and progress to their successive snail host, Schistosoma mansoni eggs must migrate from the mesenteric vessels, across the intestinal wall and into the feces. This process is complex and not always successful. A vast proportion of eggs fail to leave their definite host, instead becoming lodged within intestinal or hepatic tissue, where they can evoke potentially life-threatening pathology. Thus, to maximize the likelihood of successful egg passage whilst minimizing host pathology, intriguing egg exit strategies have evolved. Notably, schistosomes actively exert counter-inflammatory influences on the host immune system, discreetly compromise endothelial and epithelial barriers, and modulate granuloma formation around transiting eggs, which is instrumental to their migration. In this review, we discuss new developments in our understanding of schistosome egg migration, with an emphasis on S. mansoni and the intestine, and outline the host-parasite interactions that are thought to make this process possible. In addition, we explore the potential immune implications of egg penetration and discuss the long-term consequences for the host of unsuccessful egg transit, such as fibrosis, co-infection and cancer development.
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Affiliation(s)
- Alice H. Costain
- Department of Parasitology, Leiden University Medical Center, Leiden, Netherlands
- Lydia Becker Institute of Immunology and Inflammation, University of Manchester, Manchester, United Kingdom
| | - Andrew S. MacDonald
- Lydia Becker Institute of Immunology and Inflammation, University of Manchester, Manchester, United Kingdom
| | - Hermelijn H. Smits
- Department of Parasitology, Leiden University Medical Center, Leiden, Netherlands
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